Method for fabricating helical flowline bundles

ABSTRACT

A flowline bundle is twisted or braided into a permanent rope-like helical configuration, prior to laying the flowline bundle offshore by the reel method. 
     Apparatus for forming the helical flowline bundle includes a pipe twist head and a series of pipe tumblers alternating with intermediate pipe supports, which apparatus rotates and translates part of a flowline bundle while simply translating the other part.

This is a continuation of application Ser. No. 336,185, filed Apr. 11,1989, abandoned, which is a division of application Ser. No. 267,760,filed Nov. 1, 1988, now U.S. Pat. No. 4,843,713, which is a continuationof application Ser. No. 889,456, filed July 25, 1986, abandoned.

BACKGROUND OF THE INVENTION

A fast and efficient method for installing small diameter flowlinesoffshore is by means of reel, tensioner, and straightener devicesmounted on a floating vessel. However, this "pipe reel" method becomesawkward if multiple lines must be laid simultaneously, as is often thecase for flowlines laid to, or originating at, seafloor wellheads. Atypical flowline bundle to such a subsea well consists of two 3-inchI.D. production flowlines, one 2-inch I.D. annulus access line, one1-inch I.D. chemical injection line, one 1-inch I.D. hydraulic powerline and one 2-inch O.D. chemical control cable. For such multiple linesit becomes necessary to spool each line onto a separate reel, and theneither (1) lay each line separately off the floating vessel whilecarefully monitoring each suspended span, or (2) bring the separatelines together and wrap them with tape to form a "flowline bundle" whichis then laid into the water as a single entity.

Problems frequently are encountered with multiple flowlines or flowlinebundles as they are being laid or as they are being pulled-in andconnected, either to a subsea wellhead or other subsea structure, orinto a J-tube conduit on a fixed platform. Potential problems includedynamic impacts between the lines during pipelaying if laid separately.For a pull-in of a flowline bundle to a subsea wellhead or other subseastructure, potential problems include lateral buckling of the smallerlines due to bending of the bundle, overstressing of some of the linesbecause of non-uniform sharing of the tension and bending loads, andlarge torque required to orient the flowline terminal head beforeattaching to the wellhead. For a flowline bundle pulled into a J-tube,potential problems include increased pullforce due to composite-beambending effect for pipes that are tightly wrapped, differentialstretching or buckling of the smaller lines inside the curved portion ofthe J-tube, or formation of buckled pipe "loops" at the mouth of theJ-tube, for bundles that are only loosely or partially wrapped. Thepresent invention is directed toward overcoming these and other problemsof the art as will be apparent hereinafter.

Relevant prior art includes a report by Kvarner Subsea Contracting A/S,and U.S. Pat. Nos. 2,832,374; 3,197,953; 3,526,086; 607,932.

SUMMARY OF THE INVENTION

The present invention is directed to methods for fabricating flowlinebundles into a helical rope-like configuration. In one preferredembodiment, the method requires assembling a first bundle of essentiallyparallel flowlines; twisting the first bundle into an essentiallyhelical configuration; assembling a second bundle of essentiallyparallel flowlines; attaching the first (twisted) bundle to the second(untwisted) bundle with fluid-tight connections; and twisting the secondbundle into an essentially helical configuration; etc. In this preferredembodiment, the bundles are twisted into a helix at a point adjacent towhere the first and second bundles are attached. The twisting isaccomplished by rotating and translating either the first (twisted) orsecond (untwisted) bundle while translating but not rotating the other.Alternatively, the second bundle, after attachment to the first bundle,may be twisted at an end opposite to where the bundles are attached. Inanother preferred embodiment, the method requires assembling a firstbundle of essentially parallel flowlines; twisting the first bundle intoan essentially helical configuration; assembling a second bundle ofessentially parallel flowlines; twisting the second bundle into anessentially helical configuration; and attaching the first (twisted)bundle to the second (twisted) bundle with fluid-tight connections; etc.In this embodiment the bundles may be twisted from one or both ends.

In all cases the bundles may be reeled onto a reel, which reel may beonboard a vessel, and then may be laid offshore by unreeling whilemoving the vessel forward along the flowline route. Alternately, thehelical flowline bundle may be assembled into one or more long stringswhich may then be towed into place offshore by tow vessels. In a highlypreferred embodiment the parallel pipe strings to be formed into ahelical bundle are supported at intervals along the lengths thereof bytumblers which rotate the pipe strings during helical twisting thereof,and the pipe strings are individually passed through orifices of arotating twist head to produce the helical configuration of the flowlinebundle.

Other purposes, advantages and features of the invention will beapparent to one skilled in the art upon review of the following.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a helical flowline bundle formed by twisting multiple pipesand cables together into a helix.

FIGS. 1A-1D show cross-sections of the helical flowline bundle takenalone the lines 1A--1A to 1D--1D respectively as seen in FIG. 1.

FIG. 2 discloses a flowline bundle being simultaneously twisted andspooled onto a reel vessel.

FIGS. 3 and 4 disclose first and second embodiments of a pipe spoolingyard for fabricating and spooling helical pipe bundles.

FIGS. 5 and 6 disclose third and fourth embodiments of a layout of apipe spooling yard.

FIG. 7 shows a double twist head arrangement for forming helical bundlesprior to being spooled onto a reel vessel.

FIGS. 8 and 9 disclose particulars of the arrangement and connectionsbetween a pipe twist head and a sequence of pipe tumblers andintermediate bundle supports.

FIGS. 10A and B and 11A, B and C show mechanical details of a pipe twisthead apparatus including two designs of a pipe twist head disk.

FIGS. 12A and B and 13A and B show mechanical details of a pipe tumblerapparatus including two designs of a pipe tumbler disk.

DESCRIPTION OF PREFERRED EMBODIMENTS

This invention relates to the twisting, braiding, and/or wrapping of aflowline bundle into a permanent rope-like helical configuration, priorto laying the flowline bundle offshore, preferably by the reel method.Alternatively, the flowline may be assembled onshore and towed intoplace offshore without placing it upon a reel. Throughout thisdisclosure, the terms "twisting", "braiding", and "pipe twist head,"etc., have been given the special meaning of rotating the several pipesaround one another without applying substantial torque to any of thepipes, as necessary to form the pipes into a permanent rope-like helix.Thus, a line drawn along the top of each pipe in the bundle would remainat the top of each pipe throughout the "twisting" process. The onlyresidual moment or torque left in the pipe bundle after forming thishelix would be that associated with the relatively small curvature ofthe helix itself. This small torque, which incidentally, gives rise tothe forces holding the bundle together, are easily contained andcounteracted by tape wrapping means or other banding means applied tothe bundle at intervals, as described below.

A flowline bundle twisted or braided into a helix offers severaladvantages over alternative configurations. Because of the combinedweight and stiffness, and the close proximity of the various pipes, ahelical bundle provides greater strength, integrity, and protection forthe various pipes in the bundle than is possible if the lines are laidseparately. This invention enables the spooling and laying of an entireflowline bundle as a single pipeline from a single reel, such as thelarge pipe reels on various existing vessels. Thus, the need for morethan one reel, straightener, tensioner, and span-monitoring device onthe reel vessel is eliminated. This invention also permits the handling,survey, repair, etc., of the flowline bundle as a single pipelineinstead of as several separate lines, which is a significant operationaladvantage. Composite beam behavior is virtually eliminated for a helicalflowline bundle. Thus, the stiffness of a helical bundle in bending ortwisting is simply the sum of the stiffnesses of the individual pipes,which is much smaller than that of a similarly sized composite beam.Hence, the braided bundle minimizes the bending moments and torquesrequired to align the flowline terminal head with the receptacle on awellhead and minimizes J-tube pullforces. The braided bundle alsoeliminates any problems with lateral buckling of the smaller pipes dueto either bending or thermal-pressure expansion, which can occur for astraight-pipe partially wrapped bundle configuration. Thus, for example,the present invention eliminates buckling problems for flowline bundlesto be spooled onto a reel or to be pulled through a J-tube.

Referring now to the drawings, as shown in FIG. 1 a helical flowlinebundle 1 is formed by twisting multiple pipes and cables together into ahelix. The bundle may comprise, for example, two production flowlines 2and 3, an annulus access line 4, an electrical control cable 5, achemical injection line 6 and a hydraulic power line 7. When twistedhelically together they comprise a flowline bundle 1 which is stabilizedfrom untwisting by wrappings 8 and 9 of reinforced plastic tape or otherstrapping means. Experience has shown that such wrapping or strapping ofa helical bundle is strictly required only at the two extreme ends ofthe bundle, but for safety sake may also be employed at intermediatelocations.

Several different methods are envisioned for forming pipes into ahelical flowline bundle for laying by the reel method, etc. asillustrated in the figures of the drawings. One procedure, FIG. 2,involves forming several pipes 10 into a helix 11 simultaneously as thepipes are spooled onto a reel 12. For this procedure, a pipe twistinghead 13 is required, mounted near and aligned with the reel 12,optionally located on the stern of the reel vessel 14, which applies thenecessary tensions and rotations to the pipes 10 as they are fed ontothe reel 12. Pipe lengths are added to the free ends 15 of the pipebundle 11 at a pipe joining area 16 just beyond the twist head 13 fromthe reel 12. Where a fast-welding technique such as the homopolar orflash-butt methods is available, or if mechanical connections such asthreaded pipe are used, then only short lengths need be handled duringthe twisting and spooling process. However, where manual welding isemployed, the slower welding speed requires that the separate pipes ofthe bundle first be made up into long strings, and then these entirepipe strings be rotated around each other as the twisted pipe bundle isspooled onto the reel.

The rates of twisting and spooling must be carefully coordinated toachieve a uniform helix with a proper pitch length. Experience has shownthat the optimum pitch length of a helical flowline bundle is 80-100times the diameter of the largest pipe in the bundle. For a longer pitchlength the pipes are too loosely bound together and tend to separate asthey are bent onto the reel. For a shorter pitch length the pipes becomeplastically bent in the process of forming the helix, and so a straightuniform helix becomes impossible to maintain.

FIG. 3 illustrates a preferred procedure and layout of a pipe spoolingyard for assembling pipe into long strings 17, then forming these pipestrings 17 into a helical bundle 11 as the bundle is spooled onto a reel12. This procedure involves the following steps: (1) forming pipe intolong strings 17 in shop 18 by welding or other means, and placing thesestrings onto storage rack 19; (2) loading appropriate pipe strings 20from storage rack 19 into pipe string tumblers 21 and intermediatesupports 22; (3) making tie-in connections by welding or other means, atthe pipe joining area 16, between the pipe strings 20 and the free pipeends 15 of the bundle 11 from reel 12 on vessel 14; (4) simultaneouslyrotating pipe strings 20 by means of pipe tumblers 21, twisting pipestrings 20 into a helix by means of twist head 13, and spooling theresulting helical bundle onto the reel 12, while adjusting feed andtwist rates as required to maintain a proper helix; (5) stopping thetwisting/spooling operations when the trailing ends of the pipe strings20 reach the pipe joining area 16; (6) wrapping or banding the bundle 11between the reel 12 and the twist head 13 to prevent unraveling; and (7)repeating steps (1) through (6) until a sufficient length of helicalbundle 11 has been assembled and stored on the reel 12 for a givenoffshore flowline application. The tumblers 21 are preferably designedto open at the top or side to allow easy loading of the pipe strings.The rotation speed of each pipe tumbler 21 is synchronized with thetwist head 13 to maintain the pipe strings 20 straight and parallelduring the twisting/spooling operations. Back tension is maintained inthe pipe strings primarily by friction in the twist head, tumblers, andintermediate support apparatus.

FIG. 4 illustrates another preferred procedure and layout of a pipespooling yard that is nearly identical to FIG. 3, except that the bundletwist head 13 is located onshore instead of on reel vessel 14. Note inFIGS. 3 and 4 that a control cable or control umbilical 23 may be fedoff a temporary storage reel 24 and assembled together with the pipestrings 20 as part of the helical flowline bundle 11.

A fourth procedure, shown in FIG. 5, for forming pipes into a helicalbundle for laying by a reel vessel involves the following steps: (1)fabricating pipe strings 17 in a shop 18 and storing on racks 19; (2)loading appropriate pipe strings 20 from racks 19 into bundleassembly/twist area 25, which comprises at series of supports 26(preferably having rollers to allow free movement of the bundle); (3)connecting pipe strings 20 at the pipe joining area 16 to pipe endsemanating from the pipe bundle already on the reel 12; (4) connectingother ends of pipe strings 20 to a pipe twist head 27 located at the farend of the assembly/twist area 25; (5) twisting pipe strings 20 onsupports 26 into a specified helix by rotating and applying tension tothe pipe strings by means of the twist head 27 and winch 28; (6) tapingor banding the pipe strings together at the far end to preventunraveling; (7) releasing pipe bundle 20 from twist head 27 and fromclamp 29 on reel vessel 14; (8) spooling pipe bundle 20 onto reel 12while maintaining sufficient back tension with winch 28; and (9)clamping pipe bundle 20 in clamp 29 on reel vessel 14 while leavingsufficient lengths of free pipe ends for welding onto the next pipestrings. These steps (1) through (9) are repeated until a sufficientlength of pipe bundle is stored on reel 12.

A fifth procedure for forming pipes into helical bundles for laying by areel vessel is indicated in FIGS. 6 and 7. This procedure involves firstforming individual pipe strings into helical bundle segments and thenlater joining these helical strings to pipe already on the reel andspooling these helical strings onto the reel. The procedure involves:(1) fabricating pipe strings 17 in shop 18 and storing on racks 19, asbefore; (2) loading appropriate pipe strings 20 from racks 19 into acentral bundle assembly/twist area 30; (3) connecting pipe strings 20 topipe twist heads 31 and 32 at each end of the assembly/twist area 30;(4) twisting pipe strings 20 into a specified helix by rotating andapplying tension to the pipe strings by means of the two twist heads 31and 32; (5) taping or banding the pipe strings together at each end toprevent unraveling; (6) releasing the helical pipe bundle segment 20afrom twist heads 31, 32, then placing this bundle segment 20a on pipebundle storage rack 33; and (7) repeating steps (1) through (6) until asufficient total length of twisted bundle segments for a given offshoreflowline application has been produced and stored on rack 33. At aconvenient later time these helical bundle segments may be connectedsequentially at pipe joining area 16 and spooled onto reel 12 of vessel14. Finally, reel vessel 14 proceeds offshore to lay this flowlinebundle.

FIG. 7 illustrates in more detail the apparatus for twisting helicalbundle segments from both ends. For this process two pipe twist heads 31and 32, driven by motors 34 and 35, are located at each end of thebundle assembly/twist area 30, twist head 32 being mounted on astationary fixed support 36 and twist head 33 being mounted on a trolley37 with means 38 (e.g., a pneumatic cylinder) to apply tension to thepipe strings 20 as they are braided together. The assembly/twist area 30itself comprises a series of pipe supports 39a, 39b, etc., preferablyhaving rollers to allow free movement of the bundle during the twistingprocess. For any helical pipe bundling process that involves twistingpipe strings from one or both ends, as illustrated in FIGS. 5-7, inorder to produce a uniform helix additional friction reduction means(e.g., lubricants or rollers) will have to be introduced between thevarious pipes of the bundle prior to and during the twisting operation.

FIGS. 8-13 disclose in more detail apparatus for twisting and spoolingflowline bundles onto a pipe storage reel, which apparatus correspondswith the preferred procedure of FIGS. 3 and 4. Referring to FIG. 8,straight pipe strings 20 to be twisted are passed through a series ofpipe tumblers 21 which alternate with intermediate pipe supports 22,then through a special large disk tumbler 40, and finally through a pipetwist head 13. Rotation of the disk elements of each of these machines21, 40, 13, causes the parallel pipe strings 20 to rotate around oneanother as they move toward the reel 12. As the pipe proceeds from thelarge disk tumbler 40 through the twist head 13, the parallel pipestrings tend to bow out at a point 41 and then focus together at a point42 where the helical bundle becomes fully formed, after which thehelical flowline bundle 11 translates but does not rotate until itreaches the reel 12 upon which it is spooled. A variable speed motor 43is utilized to drive the twist head 13, and, by turning a series ofdrive shafts 44, the various pipe tumblers 40, 21, are turned insynchronization with the pipe twist head 13. Alternatively, one or morepipe tumblers 21, 40 may be powered by individual electric or hydraulicmotors, which are maintained in synchronous rotation with the twist head13 by an electronic control system or other means. FIG. 9 illustrates,for example, a scheme whereby three consecutive pipe tumblers 21 arepowered by a separate drive motor 45, through worm gears (not shown) anddrive shafts 44, which motor 45 is synchronized with the twist head (notshown) by electronic controls or other means. FIG. 9 also illustrates analternative type of intermediate pipe support 22 in the form of atrough, and coupling means 46 between the drive shafts 44 and thetumblers 21.

FIGS. 10A and 10B illustrate mechanical details of a pipe twist headassembly. Pipe twist head 13 and drive motor 43, together with speedcontrol 47 and speed reduction gear box 48, are mounted on a structuralbase 49, which preferably is anchored to a solid foundation. Twist head13 itself comprises a frame 50, twist head disk 51, hold-down rollers52, drive pinion 53, and drive bearings 54. Frame 50 comprises baseplate 55, side members 56, end plates 57, and roller support plates 58,all welded together. Also shown in FIGS. 10A, 10B, are drive shaft 44and coupling 46. FIGS. 11A and 11B show in greater detail two designsfor a twist head disk 51, which guides and rotates the flowlines (notshown) as they are being twisted into a helical bundle. In one design(FIG. 11A) the flowlines are guided through the inner cylindricalsurfaces 59 of two or more spherical bearings 60 which are embedded inthe disk 51. In a second design (FIG. 11B) the flowlines are guidedthrough orifices containing two or more rollers 61 whose shafts (notshown) are embedded in the disk. The disks shown in FIGS. 11A, 11B, eachcontain four orifices for twisting up to four flowlines. Other twisthead disk designs, having various numbers of orifices and/or differentpipe support features, are also possible. Also embedded in the twisthead disk 51 is gear 62 which meshes with gear 63 of drive pinion 53,shown in FIG. 11C, to provide necessary slip-free rotation of the disk51.

FIGS. 12A and 12B illustrate mechanical details of a pipe tumblerassembly. Pipe tumbler 21 consists of frame 64, tumbler disk 65,hold-down rollers 66, drive pinion 67, and drive bearings 68. Frame 64comprises base plate 69, side members 70, and end plates 71, all weldedtogether. Base plate 69 preferably is anchored to a solid foundation andmay contain screws 72 for leveling. Drive pinion 67 may be coated with ahigh friction surface (e.g. rubber), or meshing gears may be embedded inboth drive pinion 67 and tumbler disk 65, to provide necessary slip-freerotation of the disk 65. FIGS. 13A and 13B depict in greater detail twodesigns for a tumbler disk 65, which guides and rotates the parallelflowlines (not shown) which eventually are twisted into a helix (seeFIG. 8). One tumbler disk (FIG. 13A) has four orifices 73 tosimultaneously rotate up to four flowlines, whereas the other disk (FIG.13B) has six orifices 73 which can rotate up to six flowlines. Bothdisks 65 can be opened by removal of pieces 74, which are held in placeby recessed screws 75, to allow easy top- or side-loading of theflowlines. Other tumbler disk designs, having various numbers oforifices and/or different quick-opening features for loading of theflowlines, are also possible.

The pitch length of the helix for the flowline bundles described hereinis preferably equal to or less than the minimal circumference of a reelor J-tube to which the bundle will be bent, in order to avoid problemswith differential buckling or stretching of the several pipes. Thus, fora helical bundle to be laid from the reel ship Apache, the normal pitchlength is preferably equal to or less than 160 feet, which is thecircumference of the main reel. For any flowline bundle twistingprocedure in which the twisting process must be halted, the bundleremoved from the twisting apparatus, and the process later started upagain, and in particular for the procedure of FIGS. 5 and 6, describedabove, a short length at the end of each twisted pipe string ispreferably specially twisted and temporarily banded into a tighter helixthan normal. Once this pipe string has been joined to the pipe alreadyon the reel, the temporary banding is preferably released, thus forminga uniform helix across the entire pipe bundle including the sections ofpipe containing the joints between the pipe strings.

The foregoing description of the invention is merely intended to beexplanatory thereof, and various changes in the details of the describedmethod and apparatus may be made within the scope of the appended claimswithout departing from the spirit of the invention.

What is claimed is:
 1. A method for fabricating a helical flowlinebundle comprising:assembling a first bundle of essentially parallelflowlines; twisting at least part of the first bundle into anessentially helical configuration; assembling a second bundle ofessentially parallel flowlines; attaching the first bundle to the secondbundle with fluid-tight connections; and twisting any remaining part ofthe first bundle and at least part of the second bundle into anessentially helical configuration.
 2. The method of claim 1 wherein thebundles are twisted into a helix at a twist location at least near wherethe first and second bundles were attached.
 3. The method of claim 2wherein the helical twisting is accomplished by rotating and translatingthe first bundle while translating without rotating the second bundlepast the twist location.
 4. The method of claim 2 wherein the helicaltwisting is accomplished by translating without rotating the firstbundle while rotating and translating the second bundle past the twistlocation.
 5. The method of claim 4 wherein the bundles are supported atintervals along the lengths thereof by tumblers which rotate the bundlesduring helical twisting thereof.
 6. The method of claim 4 wherein theflowlines comprising a bundle are individually passed through orificesof a rotating twist head to produce helical alignment of the flowlines.7. The method of claim 6 wherein the bundles are supported at intervalsalong the lengths thereof by tumblers which rotate the bundles at thesame rate and direction as the twist head.
 8. The method of claim 7wherein the synchronous rotation of the twist head and pipe tumblers isaccomplished by a single drive motor and a series of drive shaftspassing between the machines.
 9. The method of claim 7 wherein thesynchronous rotation of the twist head and pipe tumblers is accomplishedby at least two drive motors whose speeds are controlled andsynchronized.
 10. The method of claim 7 wherein the rotation speed ofthe twist head and the pipe tumblers are controlled in relation to thetranslational speed of the flowline bundle, so as to maintain a uniformhelical configuration throughout the entire length of bundle thusproduced.
 11. The method of claim 10 wherein the pitch length of theflowline bundle helix is maintained at an optimum value between 80 and100 times the diameter of the largest pipe in the bundle.
 12. The methodof claim 1 wherein the second bundle, after attachment to the firstbundle, is twisted at an end opposite to where the bundles are attached.13. The method of claim 12 wherein substantially all of the first bundleis twisted prior to attaching the second bundle.
 14. The method of claim1 wherein the helical bundle is reeled onto a reel.
 15. The method ofclaim 14 wherein the reel is onboard a vessel and the bundles aretwisted into helical configurations on the vessel.
 16. The method ofclaim 14 wherein the reel is onboard a vessel and the bundles aretwisted into helical configurations onshore and adjacent the vessel. 17.A method for fabricating a helical flowline bundle comprising:assemblinga first bundle of essentially parallel flowlines; twisting the firstbundle into an essentially helical configuration; assembling a secondbundle of essentially parallel flowlines; twisting the second bundleinto an essentially helical configuration; and attaching the firstbundle to the second bundle with fluid-tight connections.
 18. The methodof claim 17 wherein each bundle is twisted from both ends prior toattaching the first bundle to the second bundle.
 19. The method of claim17 wherein each bundle is twisted from a single end prior to attachingthe first bundle to the second bundle.
 20. The method of claim 17wherein the bundles are reeled onto a reel.